hese can be integrated into the generic practical from the QA. Please see the discussion page to comment on these.
Salt/water absorbtion practical
Setting the scene:
Some students who were living near a tidal stream wondered whether water taken from the stream could be used for watering native plants in dry weather. They decided to investigate this by looking at how salt concentration affected the way that roots absorb water. They knew that plants can only use water if their roots can absorb it.
Your task:
You are to investigate how salt (sodium chloride) concentration affects the way that roots absorb water. To do this, you may use pieces of potato as ‘model’ roots. The equipment you will have available are:
Potatoes, cork borer
Salt, water, measuring flask
Weighing balance
Containers and lids
PLANNING YOUR PRACTICAL
You need to think about the range of salt solutions you are going to use i.e. the maximum value, minimum value, the increments You will need to justify your decisions in terms of science
You will also need to think about how you are going to measure your size of piece of potato, what size piece to use
Absorbtion of water as a percent will depend partly on surface area to volume ratio. That depends on size and shape
Sea water is about 5% salt. Saturated is about 35%. Fresh water (0%) is obviously the minimum concentration and is your ‘reference point’
Look up osmosis in Wikipedia for some theory background. Try related articles e.g. roots, salinity, irrigation, brackish, adsorption. Relating your method and conclusions to scientific theory will make the difference between achieved, merit, excellence
Investigating refractive index
Aim: To investigate the relationship between refractive index and concentration of a sugar solution. General Science information and theory background
You have learned about refractive index in the unit on physics. The refractive index of pure water is 1.33. The refractive index of solutions can vary. Your task is to determine how the refractive index of a sugar solution varies when the concentration varies.
The refractive index of a liquid can be measured by passing a beam of light through it in a transparent rectangular dish. and measuring the angle of the incident and of the refracted ray:
In this instance the angle of incidence is 50˚, and the angle of refraction is 35˚. We can assume the refractive index of air is 1.00 so the refractive index of the inside of the container is:
(sin50˚)/(sin35˚)
= 0.766/0.574
= 1.33 (as this is water in this case)
Note that there are two opportunities to measure the incident and refracted angle, on either side of the tank.
The general formula for determining the refractive index is therefore Refractive index = sinθi/sinθr
Where θi and θi are the incident (outside) and refracted (inside) angles respectively.
Note that this formula is based on the assumption that the refractive index of air is 1.00. This is likely to be close to true within the margin of error of our equipment.
The equipment available from the science laboratory will be
· To make up the solutions: electronic balance and volumetric flasks. Give the concentration in weight %, e.g. 20g of sugar made up to 100mL of water is 20%. You will need to work out a suitable range and interval for your concentrations
· To generate your refraction measurements: rectangular plastic dish, pins and laser pointer. Please make sure you are cautious with lasers not to risk the beam entering anyone’s eye, as a beam even of low power can cause damage to persons with certain eyesight conditions.
· You will need to decide what angle(s) of incidence you will use, and how many repeats. You need to explain your reasons in your report.
· You will need to supply: protractor, storage bottle (to store your made up solution)
· A good way of keeping your raw data is to trace the outline of your tank onto paper, then mark the rays as you put them in. Name and date it, an this will make up part of your logbook.
· Please keep your area tidy and deal with spillages promptly.
hese can be integrated into the generic practical from the QA. Please see the discussion page to comment on these.
Salt/water absorbtion practical
Setting the scene:
Some students who were living near a tidal stream wondered whether water taken from the stream could be used for watering native plants in dry weather. They decided to investigate this by looking at how salt concentration affected the way that roots absorb water. They knew that plants can only use water if their roots can absorb it.Your task:
You are to investigate how salt (sodium chloride) concentration affects the way that roots absorb water. To do this, you may use pieces of potato as ‘model’ roots. The equipment you will have available are:
PLANNING YOUR PRACTICAL
You need to think about the range of salt solutions you are going to use i.e. the maximum value, minimum value, the increments You will need to justify your decisions in terms of scienceYou will also need to think about how you are going to measure your size of piece of potato, what size piece to use
Investigating refractive index
Aim: To investigate the relationship between refractive index and concentration of a sugar solution.
General Science information and theory background
You have learned about refractive index in the unit on physics. The refractive index of pure water is 1.33. The refractive index of solutions can vary. Your task is to determine how the refractive index of a sugar solution varies when the concentration varies.
The refractive index of a liquid can be measured by passing a beam of light through it in a transparent rectangular dish. and measuring the angle of the incident and of the refracted ray:
(sin50˚)/(sin35˚)
= 0.766/0.574
= 1.33 (as this is water in this case)
Note that there are two opportunities to measure the incident and refracted angle, on either side of the tank.
The general formula for determining the refractive index is therefore
Refractive index = sinθi/sinθr
Where θi and θi are the incident (outside) and refracted (inside) angles respectively.
Note that this formula is based on the assumption that the refractive index of air is 1.00. This is likely to be close to true within the margin of error of our equipment.
The equipment available from the science laboratory will be
· To make up the solutions: electronic balance and volumetric flasks. Give the concentration in weight %, e.g. 20g of sugar made up to 100mL of water is 20%. You will need to work out a suitable range and interval for your concentrations
· To generate your refraction measurements: rectangular plastic dish, pins and laser pointer. Please make sure you are cautious with lasers not to risk the beam entering anyone’s eye, as a beam even of low power can cause damage to persons with certain eyesight conditions.
· You will need to decide what angle(s) of incidence you will use, and how many repeats. You need to explain your reasons in your report.
· You will need to supply: protractor, storage bottle (to store your made up solution)
· A good way of keeping your raw data is to trace the outline of your tank onto paper, then mark the rays as you put them in. Name and date it, an this will make up part of your logbook.
· Please keep your area tidy and deal with spillages promptly.